Remote control system



Patented Mar. 9, 1948 Nr OFFICE nEMoTE CONTROL srs'rEM Lloyd V. Lewis,Pittsburgh, Pa., assignor to The Union Switch 8a Sign al Company,Swissvale,

Pa., aV corporation of Pennsylvania Application November 1o, 194.4,sena: No. 562.85

My invention relates to remote control systems,

and more especially to .apparatus suitable for use in centralizedtrailic Vcontrol systems for railroads. Y

In systems of this character, as Villustrated by y9 claims. (ci.177-353) Letters Patent of theUnited States Nos. 2,303,875 and2,350,668, for example, it is .customary to provide a code typecommunication systemfor controlling track switches and railwaysignalsover an extensive stretchA of territory by means of codes of directcurrent impulses transmitted l from the dispatchers olilce,'andv toprovide a dispatchers telephone line usually using the same line wiresby means'of which the crews'of trains at various Way stations may`Vcommunicate with the dispatcher. A selectivecalling system is also f nneeded in order to enable v'the dispatcher to establish telephonecommunication with the field stations, and since the selector systemscommonly used employ codes of low frequency impulses which are of sucharcharacter as to interfere with the operation of the centralized traiccontrolling system it has beennecessary to providemeans for suspendingthe operation vof the latterwliile the line is in use -forselective'calling. `Furthermore, the selectors present an additionalload 4on i the line circuit for Ythe centralized traiiic control system;and forthese. reasons the selector system decreases the capacity'lof4the centralized traliic control systemy to 'some extent even though thetwo' systems arefnon interfering.

OneV object of my invention is the provision of aV code system of remotelcontrolsuitable rfor selective calling or the like which 'employs'codes of alternatingv current impulsesfof different frephone linewithout interfering with the transmission of low frequencygcode impulsesover the same line. Y Y l f Another4 object of my invention isV theprovision of a. remote control system particularly suitable for. use forthe control and'indication of outlying traiic' governing devices, suchas velectric switch locks. for handthrow switches. thefcontrol of whichheretofore has required the installation of line'wires ofteneirtendingseveral miles from the switch locationrto the nearest eld stationof thecentralized traic control system.

My invention, `is an, improvement upon that disclosed in applicationforLetters Patent of the United States Serial No..514,641, filedDecember 17, 1943, now U. Letters Patent y2,396,134 granted March 5,1946, by A. J. Sorensen, for Remote control systems. Y Y

A feature of my inventionis the provision of V quencies suitablefortransmission over a'tele-l-Y 2 Y code receivers responsive to aplurality of frequencies and connected to aline through different tuned`circuits, vone circuit atV a time, so as to present a high impedance tothe line.

Another feature of my invention is the provision of code receivers ofthe electronic type which areY normally deenergized and employ localsources of' direct Vcurrent as their sole source of energy vso that theymay be efficiently employed at isolated locations, with infrequentmainte- Il shall describe one form ofapparatus embodying ymyinvention.land shall then point out the novel features thereof in claims.

vReferring tothe accompanying drawing, the reference characters Y and Zdesignate a pair of line wires which provide a communication channel formy remote control system extending from a control oiiice equipped withtransmitting apparatus as shown inthe lower portion of the drawing,through arplurality of stations located at spaced points valonga stretchof railway at each rof which areceiver similar to the one shown inthe'upper portion of thedravving is located. Each receiver is adaptedrtocontrol an electro-responsive devicesuch/as a bell orbuzzer BZ, or themagnet WL of an electric switch lock, or the like.

The system of my invention employs alternating currentvcodes each`comprising a series of steps marked byV periodic changes in thefrequency of the line current, without interposed pauses, each-frequency combination comprising astation code call.l In its specificembodiment as shown herein,;ithe system is arranged to use vefrequencies', designated ,fl to f5, and three code steps.:,- Thefiirstcode'step may have any ,.oneof'vefrequencies. Any one of the four notused for the first step are available for the sec- VondV sten-and anyone of the four not used for thegsecond stepY may be usedfor the thirdstep,

' providing 5X4 4=80 dierent code calls for the selection ofthecorresponding number Vof stations. The frequencies may be in or abovethe yvoice frequency .band depending upon the circuit requirements. Inthe form shown herein, the

line currents are generated by an oscillator tube `Vicorltrlledbya'tuned circuit comprising a coll`L3 having an adjustable number ofeffective turns and a condenser C3'so las to deliver any one of the iivefrequenciesv fl-f. The tube V3 controls anampli'er tubeV V4 by'which thealter- 'nating current yoftheselected frequency is delivered through acoupling transformer L4 to the line'wiresY and Z. The transmittingapparatus includes aserlesof push buttons or keys PI-P80.

to respond selectively fl,- f2, f3; as-indicated by sponsive areindicated by the references jacent the transformer connectionson t ings,and-as shown, the front contacta of key 1 P2 is connected-toamire"marked fl, ,indicating that coil L3 and. condenser C3 are. tuned tothatassiste Each station receiver includes lve relays-Rij and S2, twoelectron tubes VI land: V2-

R2, L, Sl

of the cold cathode, controlled ionization type,

and V4. Tubes V3 and Vit shown. Theplate; c

so that tubes:

. 1 Thafreguency of 4 rent of frequency fl and to supply it through tubeV4 to the line.

When relay TI picks up, the energizing circuit for relay T2 is opened.Relay T2 releases after a suitable interval and shifts the connection ofthe positive terminal of battery B3 from contactd of key-P2 toytliebranch .circuit including Vfront` Contact b` of -r'elay T3,backcontact c fQi key PI and front contact c of key P2, tuning thecircuit L3-'C3 to the frequency f2..

the line current thus shifts to another upon the release romA onefrequency ---of--relay-T2j, the-second frequency being deter- Y dby;the-cornection to contact c of the "operated key,

this being lfrequency f2 in the case 5 1 beine. :described-:15.

and a transformer LI having an adjustable pri-wL mary tuned by condenserC2 connected across the line andan adustable secondary turned bycondenser-CI; by means of' `which-the--r'ec'eiver-at eachstation --isrendered selectively responsive to a distinctive sequence-offrequencies-supplied to the line by the operation of thecorresponding Each station-is provided-With the usual local lbatteryhaving-the terminals-B and C for energizing the-relays L,"'S|'-and S2,andthe buzzer arid---f-or supplying an answer back signal to the line inresponse to the operation-'of *the electr-icswitch-lock conltrolleol bymagnet-WL--and-has a second battery BI for energizing-theelectron-tubes--VI and V2 The station-apparatus 'as-shown is connectedto--the code combination the connections to contacts b and c Lof relaysS 'and-therelays Rl and R2 connected in series l and VSL-the` oiiice keyJWhichisi-similarly 4fconriec-tefsl and- Which therefore controls-thestation shown-being the key. P2.

- I-t-is believed that my-invention may be most --readilyunderstood--fromwawdescription .of rits mode ofoperation,and-accordinglyfI--shall now assume that theop'eratorI-presses-the key P2 to operate -acalling-device illustrated asa buzzer BZ- at thestation-shovvn il c The closing Aof -contact a--ofkeyP2 completes a-circuit-from:terminal-B-ofthe local sourceofwcurrent-over back contact-a ofrelay TI through -relay- TZ--toterminal- C. Relay-'T2 --picksup 'and byclosi-ngits contact-a en-ergizesrelay iT?.

y which turn closes-itscontacta to-energize relay Tl. Y y Relay .pickedup-aslong as the `Vtery B3 .through the primary of transformer L4 T-I.completes astick circuit at its con- '-tact a so that itis-held key-P2is pressed; and closes-:a circuit `from the `positive terrninalv ofbattery: B3. contacts bof relays.l Tlof keyPl and iront contact d.. ofvkeyPZthroughs;4 the primary-:of transformer- L3 tube V3.

to the plate of tube V4, and the closingl of contacts c and d of relayTlconnects the :secondary of transformers-L4,-throughf the condensers C4across the line .wires-:Y and Z.- `Thefrequency to which the adjustabletuned circuitsrarerethe draw- P2, therefore, tube V3 is caused togenerate cur- When relay T2 releases, it opens the energisirgciroult forrelay T3, and the second frequency is supplied only untill. relay T3releases, after which thevfrequency-lis-.'again. shifted, thefrequency-,lof the -third nimpulse `being ,determined --by theconnection-,to ,contacth of-the operated key, this being frequency f3when key P215 operated, or wfrequency .fl .Whenkey Pl .is operated, as!will be Aseenfromthe. drawingthe third impulse-.being terminated., bythe ,release of relay Tl lfollowing. the releasecf the operated key.

Each code thus-comprises a sequence ofthree ,impulsesv Without interposed;pauses, the last of which, comprisingthe operating .or deliver'y`impulse -ofthe; code, may be .prolonged as long as desired'byholding.the operated- `keyl depressed.

- Considering -noyvY -ifl'i-e.- station apparatus, it is ftobeeunderstood that-thesprimaryof ltransfer-'mer .Ll is tuned bycondenser G2 and presents a rela- -tively highy impedance;- 13o-,theline,v and that due `to line losses, thetuningis somewhat broadso-thatifrthis Wieregthe onlytunedY circuit provided, :the receiverwouldrespond, `more or less to a iband `of, frequencies; .asi required` forcertain application-S, Ias ,illustrated-,- for-example, by Letters f4Patentfof the-.United Statesbld 2,272,786, granted February10,--,19l;2,toNornjranA. Agn-ew. `In accordance with :the requirements `of i thepresent fi-nventiom asharper selectivityds required, and -vthis-isaccomplishedgby-.the provisionof a second tuned circuit, comprising-aloosely coupled low resistance secondaryiortransformer Ll whichis-,tuned-/byacondenser Gl., y -f Normally-, :transformer-Lt is tuned,by circuits `completedover back-.contacts b vand c-V of there- .laysf-SI1. and 152,1 and-at;` the station shown these aretuned tothefrequency`fl, so thataresonant n.voltage -.,is`V developer-l-` across. .theterminals of `condenser Cl1whn current of that frequency issupplied-.tothe 1ine'.;fc- Y, f Relay `R tais Vconnected-.1in kseriesywith the' 4plate circuit of tube Vl across battery BI, the voltage vofwhich is, insuiiicien't to start ionization 4of the wtube VI,consequentlyrelay RLis normally deenergized adjustable posltivepotentialderived fromcbatteryv-Bl .issupplied-to the grid of --tubeVl inseriesWiththe alternatingpotential across-,condenser C:I,-,due-.t`o.y the linecurrent, by zmeans Vofwhich.ionization-is caused to star-tin responsetolline current-of the proper value and frequency, so astocause theplatecircuit. of tube lVl tobecorne:conducting-,and relayRl to becomeenergized. L'Ihecvol'tage appliedV to the plate circuitbybatteryBLalthough,insufficient to start ionizatioma-,is.c'apable'fmaintaining the tube in thecOnducting- 'condition-.so as; to.hold relay R I energized after the tube.is, .once fired by theapplication fof.- thelproper. positive :potential to the grid circuit,even though this potential is applied butiinomentarily.' .and it isnecessary to deionize thev tube before itcan` again serve as a detector.`This is accomplished by including a back contact of relay Rlin theplate circuit so that as soon as relay RI becomes energized the sourceof current BI becomes disconnected, tube VI becomes deionized andrelayRlreleases.

Relay Rl therefore 'responds but once to a single positive impulseapplied to its grid circuitl and operates repeatedly only in the event asustained resonant A. C. voltage of a predetermined value is presentacross condenser Cl.. As used in practice the constants of its circuitare such that relay RI vibrates at the rate of about twenty times persecond.

In order to differentiatev between-the random operation of relay RI, dueto. impulse or shock excitation or the like, and periodic operation inresponse to sustained oscillations, a second tube V2 is provided. Eachtime relay Rl is energized, the potential of battery Bl is appliedacross a f resistor r4 ,of relatively low, value and v in seriestherewith, a condenser C4 anda resistor r2 having ahigh resistance, inparallel. The potentiall acrosscondenser C4 is applied through relay R2to theplate of tube V2 and a positive potential derived therefrom isapplied overan adjustable connection to resistor r2 to the grid of tubeV2. When relay Rl is energized, condenser C4 charges at a ratedetermined by the product of thevalues ofr4 and C4, and when relay Rl isreleased, condenser C4 discharges slowly through resistor r2. Thepotentials thus applied to the grid and plate circuits of tube V2increases step by step in response Vto the vibration of relay RI untilthey reach valuessufl'icient to cause tube V2 to fire Vwhereupon relayR2 bec'omes energized. The energy stored in condenser C4 causes currentto continue to flowthrough relay R2 duringthe intervals when, due to itsvibration, the

front contact a of relay Rl is open, so that relay R2 is held picked upas long as relay R l continues to vibrate. When relay Ri ceases tooperate, condenser C4 discharges and tube V2 is deionized so that relayR2 releases following a relatively short pause in the operation of relayRI Y kAt each stationresponsive to a 4first code step of frequency fltherefore, relay Rl vibrates and energizes relay` R2, whichin turnenergizes a slow release relay L over its front contact a. When thefrequency Vof the line current is shifted to the second frequency f2,the energized relays RI cease tovibrate and the associated relays R2release, for the kreason that the impulse of frequency fl to which thecircuits for these relays are adjusted.V to respond has been terminated.Each such relay R2 then closes a pickup -circuit for a rst steppingrelay Sl which extends from terminal Bat contact a of relay L oyer backcontact b of relay R2, `back contact e Vof relay S2` through relay Sl toterminal C, so that relay Sl becomes energized. v

Assuming that there are eighty stations, arranged in flve groups withrespect to the frequency towhich they respond on the rst step, thereceivers at sixteen stations will operate as described, and of these, agroup of four will have the tuning circuit which include front contactsvb and c of relay SI connected so as to respond to'frequency f2. At eachstation of this group, when relay SI picks up the tuning adjustment atthat station is shifted from frequency fl -tothe frequency f2 ,which isbeing supplied to the line at the time and consequentlyrelays Ri and R2become reenersized. t hold the slow release relay 6; L picked up, while.at the others relays RI and R2 remain released 'so that their relays L'and SI release.V Each energized. relay R2 completesra stick circuit forrelay SIv extending from terminal B at contact a of relay L over frontcontact b of relay R2 and the front contact a and winding ,of relay SIto terminal C, and vcompletes a pick-up circuit for the second steppingrelay S2 extending from terminal B at contact a of relay L over frontcontact c of relay R2, front 'contact d of relay Sl and the winding ofrelay S2 to terminal C so that relay SI is held energized and relay S2picks up on the second step. e When the frequency ofv line current isshifted to the third frequency f3, the termination of the impulse offrequency f2 causes the relays RI and'RZ to release at each of the fourstations at which relaysSI and S2 are energized, and each such relay SIreleases, due to the opening of its stick circuit at contactb of relayR2. Each energized relay S2 is held picked up by relay L over a stickcircuit-,including its front contact a.

It will be understood that at each station of the selected group,thetuning circuits which include the back contacts b andc of relay SI1and the front contacts band c of relay S2 are differently connected,those at only one station of the group being arranged as shown in thedrawing to respondto frequency f3. At this one station,

Vtherefore, the release of relay SI vdue to the termination oftheirnpulsefof frequency f2 shifts the tuning adjustment from frequency Vf2to the frequency f3 whichat this timeis being supplied to the line, andat that station, relays RI and R2 are'reenergized to hold relay Lenergized, while at the others relays RI and R2 remain released so thattheir relays L and S2 release.

At the selected station, the response of relay R2 to the third Vstepcompletes a delivery circuit extending from terminal B at contact a ofrelay L, front contact c .of relay R2, back contact d of relay SI, frontcontact d of relay S2 throughv buzzer BZ to terminal C. The buzzer" BZvv at only one station is thus sounded selectively in response to theoperation of the corresponding rkey P2, and continues to sound until thekey P2 is released.

It will be understood that the apparatus at those stations arranged torespond to arst frequency f2 or f3 will respondto the second or thirdfrequency of the code described but at none of these will the deliverycircuit be closed, and at the end of the code theapparatus at thesesta-v tionswill be restored to normal after responding to only oneor twoof the code steps,

It will be seen thatthe number of tuned cir? cuits which are resonantAto the line current at any given time is relatively small in comparisonwith the number of stations, consequently the impedance presented by theapparatus to the line may be made. suiciently high to adapt the systemreadily for use on electrically long lines.

Considering now ther application of the system of my invention tothecontrolrof anelecf tric switch lock; the'diagram at the upper rightin the drawing indicates a portion of railway track Vwhich includesahand throw switch W, the unauthorized operation of which is preventedby the provision of an electric switch lock. This device, as shown, isVto beunderstood to be of the type shown in Letters Patent of the UnitedStates No. 1,126,834, issued VFebruary 2, 1915, to Neubert etal.,comprising `a rotatable shaft car-j rying a Vsegment 25 and two contacts46 and 48, whichshaft in the ,nesltignhvwn Altkethe;er:

segment 25 theoper -vguishalole from the'freguency ,V3, assuming thelatterhtolb nthe -audio erating nleverv 8 zof. the swltchtsinl.risposi-tions to maintain the trackziswitch- W..?l'ock.edf. normal',While the shaft-.in turnlslocked inthe position shown .by .apadlookzhavingraibail. 50.:`

To unlock `the svvitcli` the- .padlockmust.flrst be removed .by thetrain. crew,.. aftenbbtaining .permission .by telephone. from. theoperator at .the dispatchers oice,il.thuspeimitting .-ithez-segment to`-bemoved a short-.ldistance-taipositiornto engage the locking dog'21u-andato close. contacts 46441". Then if traffic '.conditimsA .are.proper -as indicated by the energizat'ion .of airelafy-TR, a magnet WLmay be energizedbverga oircuitinf cluding contacts l 464-411tollifti-the i.lock-ingdog 214, permitting 'segment 25.to: be-'movedgto.itsl full reverse position inwhicn-the-sWitcndever 8. is `free to beoperated.-

Itis .desirable toinsurethat the'operations described are carriedlout.only-=withlthe knowledge and 'cooperation' or the central oilice1operator; and this rnayv readily be.: acco-'mplishedby con.- trollingmagnet WL overthe-delivery circuit; of my receiver` as shown.4

In accordance Withthe preferredmod'eof operation, a member of the trainecrew advises the operator by telephone-When he isi'eady to reverse iatop then presses .key P2Y to selectively energize the delivery circuit'and cause buzzer BZ-tfsound l at the location ots-witch Wg?. therebyinforming 'the train crewA that the switch is electricallyhunlocked, and`energizing magnet WL When 'contactsilB-I-izarel closed by the'l traincrew.v When theAbuZzer-signallisheard, therefore, theV segment-may.- bemovedto full reverse, whereupon the closingof contacts 48-49 connectsterminals B and C offV the "local source of current across the KlinelWires through resistors r5'and condensers C5',` theconnection'coin-prising a 'branch 0f the delivery' ciruit--wmninciudesin addition, a iront'cot'act Y1;"o-i relay-RI. Y.A variablepotentialthus' appliedto the Iline dueto'the vibration of-` relayRlxvhleriproduces an audible ansvver bac Vsig'aAl` iny Vtldewo'peratorsloudspeaker ILSlvvhich readily distinrange.

The loperator therefore* holds the key V'PZi pressedfuntll the answerAbaclffsigival is'received, indicating that thfunlocling operations havebeen completed.WT "N Itis to be noted that the answer backv impulsesimpressed uponthe l'i're by thefhclosingqof'front contact b ofrelayR'l-"are incapable -ofcontrolling the tube VI so as tofcontinue'rl'z'i'y7R11-,vibra-v tion 'after key' l2fis'V` releasil,` corresponingV to the mode of operation"dscibedin-fthe Agnew patent hereinbeforereferred' to, for ftloereason that 'the impulses are applied tofut'heline over front contacts 'bof relay Blot-,1ay time `v'vhn tube VI' isV deenergized by the opening fbik contact aof relayfn|.

Although I have herein shown and vdescribed only one form of remotecontr d`lsystern"enibodyQ ingwrny invention; itis uhd/Mstoodthat variouschanges and modificationsniay be made therein within the scop'eoftneappndeddiaiips 'without departing from the spirit and?,scc'ipiffnl'yinvention. A f,

Having thus described invention, what; clai'mg, l

l.' Ina remote control system having aV pair of line` Wires to whichdifferentcodes-are"sup1olie :it each 'Comprising ia? entre??tif-.alternates sur# rent impulses "of- 'successively l"difieren-tffrequencles, a. receiver .including .a plurality. off ftunedcircuitszeach. tuned 4to a ,diierent frequency and each ...coupled to asharply tuned. localwcircuit tuned Vto .the same frequency fordetermining the frequenciesof the line current towhichsuch receiver isresponsive;` and stepping `means controlled by said receiver in responseto the code impulses forconnecting said-tuned circuits across thelinewires only one .atta time andforsim-ultaneouslyfconnecting the localcircuits-tuned to the corresponding. frequencies to said receiver vonlyone at a time to renderA vthe receiver-responsive to a distinctivesequence ofA impulses constituting a code call.

2. In a remote control system having-a pair'of line-Wiresto-Whichdifferent codes are supplied each --compr-ising a sequence of-alternating V curren-timpulsesof' successively *different` frequencies,a receiver including ani-adjustable tuned circuit connected to the lineWires iorgoverning its operation,A said tuned circuit-being 4normallyadjustedl to vrender the n receiver selectively responsive"-tolinecurrent having a selected one ofY said frequencies, stepping meanscontrolled "by said receiver and Yacting in response to theterminationvof'an impulse oi a particular frequency to change theadjustment oi said tuned circuitrto renderV the receiver-selectively-responsive to the next impulsewof a distinctive sequence ofimpulses constituting a code, and a delivery4 circuit prepared by saidsteppingmeans-and closed by said receiver in response to the lastimpulse of said code.

. 3. Inl a remote control system, a receiver responsive toa sequence ofalternating current impulses of' successivelydiierent frequencies',cornprisingfa receiving relay, an electron tube having an inputcircuitsupplied with said impulses over one of a'plurality of tuned circuitseach tuned to a different-,one ci said frequencies, and anoutput circuitfor controlling said receiving'relay, a series of stepping relays, aslovv release relay., means controlled'by said receiving relay forintermittently 4energizing said slovv release relay to maintain itpicked up as long as the receiving relay continues rto respond to saidimpulses, meansicontrolled jointly by saidl receiving' relay and byvsaid-slow release relay for energizingsaid stepping rrelays one'at atime to count' the impulses; means controlled by said steppingrelays forconnectingV theV` grid circuit of Vsaid tube to different' onesof'sa-id-tuned vcircuits kone at a time torender--said receiver'responsive to a distinctive sequence of impulses constituting a stationcode callgand a delivery circuitjprepared by said stepping relays andclosed"bysaidreceivinggrelayf,in

response to Vthe lastjimpulse Vof said' distinctive sequence.

4. Ina -rernotej,control systen1,)a receiver respon;4 ive to-a ysequenceof4 alternating currentl impulses of successively different frequenciessupplied to ,a liney circuit, comprising a line-relay `controlled` bysaid impulses and a series of stepping relays operable one at a time invorder in response tofdiierentoperations oftheline relay to2-countl 'theimpulses as received,l 'means comprising aplurality' ofadiustable tunedcirfcuits for rendering the line relay responsive only to'linecurrent ofa particular one ofsaid'frequencies, means controlled by i said steppingf. relays iorfshi-ftling `the connections ofv saidl tuned circuits tocondition vthe 'line relay to respond to successiveimpul'ses ofld'iferent frequencies,V and a VdeliveryP circuit 'closed-bythelinerelay and by thelast' stepping relay of the vser-ies A'-v'vhen-vsaid lineV relay has responded 'to a predeterminedli number of impulses.l

5. yIn a remote control system, a receiverresponsive Ato a code ofalternating current iinpulses of successively different frequencies,comprising any electrontube having a plate circuit connected to a localsourceof current and a grid circuit to Which said impulses are supplied,a

receiving relay controlled bythe current in said plate circuit,aplurality orf-tuned circuits yeach selectively responsive to a diiferentone ofsaid frequencies one of which circuits is normally interposed insaid grid circuit to render said tube effective to operate the relay inresponse to the first impulse of a code only when suchimpulse is of thecorresponding frequency, adjustable connections controlled by said relayfor interposing different ones of said tuned circuits in said gridcircuit successively as the impulses are received, said connectionsbeing arranged in a distinctive code pattern corresponding to a code ofimpulses identifying said receiver and serving to render the tubeeffective to operate the relay in response to the succeeding impulses ofsaid code only when they have said distinctive code pattern, and adelivery circuit closed by said relay only when it responds to the lastimpulse of said code.

6. In a remote control system, a receiver responsive to a code ofalternating current impulses of successively different frequencies,cornprising an electron tube having a plate circuit connected to a localsource of current and a grid circuit to which said impulses aresupplied, a receiving relay controlled by the current in said platecircuit, a series of stepping relays controlled by said receiving relay,a `plurality of tuned circuits each selectively responsive to adifferent one of said frequencies one of which cirl cuits is interposedin said gridy circuit to render the tube effective to operate the relayin response to the first impulse of a code only when such impulse is ofthe corresponding frequency, acljustable connections selected by theoperation of said stepping relays for interposing different ones of saidtuned circuits in said grid circuit one for each operation of saidreceiving relay said connections being arranged in a distinctive codepattern corresponding to a code of impulses identifying said receiver,and serving to render the tube effective to operate said receiving relayonly so long as the received impulses conform to said code pattern, anda delivery circuit prepared by said stepping relays and closed by saidreceiving relay when it has responded to each of the impulses of a code.

7. In a remote control system, a receiver responsive to a code ofalternating current impulses of successively different frequencies,comprising an electron tube having a plate circuit connected to a localsource of current and a grid circuit to which said impulses aresupplied, a receiving relay controlled by the current in said platecircuit in response to said impulses, a series of stepping relays,circuits controlled by said receiving relay for operating the steppingrelays one at a time in order to count the impulses as received,adjustable connections controlled by said stepping relays forinterposing differently tuned circuits in said grid circuit, one foreach impulse, to render the tube effective to operate the receivingrelay in response to the successive impulses of a code only when theirfrequencies have a particular pattern constituting a distinctive codecall, and a delivery circuit prepared by circuit supplied with codeseach comprising a sequence of alternating current impulses of suc.-

cessivelyl'fdifferent frequencies, a receiver comprising anelectron-tube having a plate circuit and a grid circuit, a receivingrelay controlled` by current supplied to saidV plate circuit, aplurality cfprimary tuned circuits each responsive to Va differentfrequency, stepping means controlled by said receiving relay, meanscontrolled by the stepping means for connecting said primary tunedcircuits to the line circuit one at a time in order, a plurality ofsecondary tuned circuits each responsive to a different frequency andeach coupled loosely to that one of said primary circuits which is tunedtothe same frequency, means controlled by the stepping means forconnecting each secondary tuned circuit to the grid circuit of the tubewhen the corresponding primary circuit is connected to the line circuitto render the tube effective to operate said receiving relay; and meanscontrolled by said receiving relay When it releases upon the terminationof a code impulse of a particular frequency for operating said steppingmeans to change the connection of said tuned circuits to render the tuberesponsive to a succeeding impulse of another particular frequency.

9. In a remote control system, a code receiver responsive to a sequenceof alternating current impulses of different frequencies, comprising afirst electron tube of the controlled ionization type having a platecircuit normally connected to a source of direct current, a receivingrelay responsive to the current which flows in said plate circuit whenthe tube is ionized, a grid circuit including tuned circuit elements forcausing the tube to become ionized to effect the energization of saidrelay when alternating current of a particular frequency only issupplied thereto, means for deionizing said tube comprising a backcontact of said relay in said plate circuit for interrupting the ilow ofcurrent when said relay becomes energized causing said relay to vibrateas long as alternating current is supplied to said grid circuit, asecond electron-tube of the controlled ionization type having a platecircuit connected to a source of current over a front contact of saidreceiving relay, a second relay responsive to the current which flows inits plate circuit when said second tube is ionized, said second tubehaving a grid circuit connected to a condenser which is charged througha resistor by the repeated operation of said receiving relay for causingsaid second tube to become ionized to energize said second relay only inresponse to the sustained vibration of said receiving relay, a series ofstepping relays, circuits controlled by said second relay for operatingsaid stepping relays one at a time to count each alternating currentimpulse as received, means controlled by said stepping relays forchanging the connections of said tuned circuit elements as each impulseis received to render said first tube responsive only to current havingthe frequency of the next impulse of a particular code, and a deliverycircuit prepared by said stepping relays and closed When said secondrelay has responded to each of the impulses of said code.

LLOYD V. LEWIS.

(References on following page) 2,131,164 Chauveau .,S ept. 27, 1.93.8: 5

The following references are of record'inthg @157539,542 Bemam sept 19,1939

